We welcome the study by Krogh and colleagues (Krogh, Videbech, Thomsen, Gluud, & Nordentoft, 2012) and commend their attention to detail in terms of compliance with the CONSORT guidelines for conducting randomised controlled trials. The findings relate very specifically to aerobic exercise versus an attention control of stretching activity over a 3 month programme but there is not a no treatment or usual care comparison. The results showed no difference between the two groups at 3 months in terms of depression. The authors conclude that the results do not support referral to aerobic exercise for depression. The design used seems plausible and ethical but we believe that there is a potential flaw that could lead to the wrong conclusion. When we look at the results we see that both groups decreased depression scores in the same way. Without a no treatment or usual care comparison we really cannot make conclusions about effectiveness or lack of effectiveness of aerobic exercise. In a similar trial design, but with the inclusion of a usual care comparison, we looked at the effect of aerobic exercise on quality of life for women treated for breast cancer (Daley et al., 2007). In this study the aerobic exercise group improved versus the usual care group but not in relation to the placebo [or attention] control group. The placebo group also had some improvements against the usual care group. We concluded that our results showed clinical levels of improvement but we would not have been able to make that conclusion without the usual care comparison. We now think that even what we might have considered as a placebo or attention control condition involving predominantly stretching activity is probably not an ‘inert’ treatment. This may be particularly true for people who have not been active for some time for whom even the warming up activities needed for safe stretching create a increase in activity over resting levels. Thus even these very low levels of activity may be helping depressed patients with how they feel and we might therefore equally conclude from the Krogh study that both aerobic and stretching activity might be helpful for patients with depression. International guidelines on how much activity people should do to gain health benefits (including mental health benefits) suggest that while a minimum dose is recommended (typically 150 minutes of moderate intensity activity over the course of the week) we should all be aware that there is a dose response curve associated with these benefits (Global Advocacy Council for Physical Activity International Society for Physical Activity and Health, 2010). Therefore, even doses of activity, such as that achieved via a stretching programme, may confer some benefit.

We commend the authors future research ideas as stated in the paper and hope that they take this discussion of design and the use of a stretching group as an attention control into account.

Daley, Amanda J., Crank, Helen, Saxton, John M., Mutrie, Nanette, Coleman, Robert, & Roalfe, Andrea. (2007). Randomized trial of exercise therapy in women treated for breast cancer. Journal of Clinical Oncology, 25(13), 1713-1721.
Global Advocacy Council for Physical Activity International Society for Physical Activity and Health. (2010). The Toronto Charter for Physical Activity: A Global Call to Action.
.
Krogh, J., Videbech, P., Thomsen, C., Gluud, C., & Nordentoft, M. (2012). DEMO-II trial. Aerobic exercise versus stretching exercise in patients with major depression-a randomised clinical trial. PLoS One, 7(10), e48316. doi: 10.1371/journal.pone.0048316